SMA (Shaped Memory Alloy) is an alloy which, when deformed, returns to its original shape if heated, “remembering” its original form. When the shaped memory alloy is in its cold state, the metal may be folded or stretched in various shapes, which will be maintained until it is heated above the transition temperature. After heating, the shape changes, returning to the original. Said alloy has been used as a connection for tubes for coupling or junction in subsea environments, substituting the orbital welding process which is commonly used.
The shaped memory effect in nickel-titanium alloys was disclosed for the first time by Naval Ordenance Laboratory, in 1962. In 1963, a coupling for 6000 psi pressure was projected and qualified for surface vessels of the Royal Navy. In 1969, an application was disclosed for 3000 psi pressure coupling, appropriate for a fighter jet F14 from the U. S. Navy. In 1975, the system was extended for nuclear submarines of the Trafalgar class. Nowadays, couplings based on shaped memory alloy are used by companies in the aerospace industry in airplanes (Boeing®, Airbus®, Cessna®, Learjet®, Bell® Helicopters and many others), and in the tubing, automotive, telecommunication, robotic, medical and motor industries.
Subsea Christmas trees are used in oil and gas fields. A subsea Christmas tree monitors and controls the production of a well, managing fluids and gases as injected into the well. Subsea Christmas trees have various tube connectors, requiring connections to be sufficiently efficient to avoid leakage. In production lines, the orbital welding process is frequently used for the connection of hydraulic tubes, but there are a few problems during this process, including e.g. a special preparation of the tubes, use of specific machines to be employed for orbital welding, qualified staff, a complex welding procedure, post-welding preparation, visual inspection of X rays including the whole preparation process, a wide workspace and a huge time to perform the operation, among others.
Therefore, considering that the orbital welding process represents about 50% of the hydraulic instrument schedule to assembly a Christmas tree and considering workflows which are usually very crowded, solutions involving better use of time and less cost should be especially preferred.
Therefore, despite subsea tube orbital welding still being currently used, the shaped memory alloy represents a new solution for submerse tube coupling, since, besides reducing the problems as indicated above, it provides advantages such as:                the tension of the connection is not affected by vibrations or impacts;        the assembling time is insignificant in comparison with orbital welding, since it requires just a few minutes;        increase in work safety;        work with X ray inspection is dismissed;        no requirement of highly qualified staff;        no requirement of constant training for technical staff for qualification for the service; and        reduction of about ⅓ in the total cost of the operation.        
The patent EP 0632224B1 presents a solution for subsea couplings or connections embodied by means of a configuration comprising an anti-corrosive material around the tube, followed by the memory alloy covered by the same material of the tube, to avoid galvanic corrosion and weakening by hydrogen. That solution, despite using shaped memory alloy, has an inconvenience related to the requirement to perform material deposition over the shaped memory alloy, and that material should mandatorily have the same composition of the tube, since, if different, galvanic corrosion will occur and any fault in deposition will make the material susceptible to corrosion. Furthermore, special attention should be given to the thickness of the deposition of the shaped memory alloy material, to avoid the flexibility of movement of the relaxing material and its contraction from being compromised, which would damage the connection.
Therefore, so to definitely solve all the problems as indicated above, a connection using shaped memory alloy material of the present invention has been developed, which is used in subsea Christmas trees or any other subsea devices requiring tube coupling, even in the presence of corrosive water and a wide range of hydraulic fluids and chemicals, both in the internal and external environment of the tubes.